In June, while the well resisted control, scientists led by David Valentine, a microbial geochemist at the University of California, Santa Barbara, took several hundred samples of natural gas at 31 sites in a large circle around Macondo, extending to a maximum of 8 miles from the spill's epicenter. Data from their cruise, sponsored by a grant from the National Science Foundation, amount to the first independent snapshot of the immediate, short-term response triggered underwater by an onslaught of gas.

The majority of the methane, they found, remained dissolved more than 2,600 feet underwater, and the gas likely accounted for two-thirds of all the microbial activity in the undersea plumes. Based on government and BP data, some 206,000 metric tons of methane, 35,700 tons of ethane and 28,400 tons of propane snaked out into the subsurface, they estimated.